Enucleation or evisceration of the eye is performed because of disease or trauma that make the removal of the eye, or the intraocular contents of the eye, necessary. Following such a procedure, the patient normally desires use of an artificial eye to restore a more normal appearance. To satisfactorily fit an artificial eye into the orbital socket, an orbital (herein also called an "ocular") implant must be placed within the orbit to replace the volume that was lost when the eye or its contents was removed. However, the use of an orbital implant and the subsequent fitting of the artificial eye confer more than a cosmetic benefit. They help maintain the normal structure of the eyelids and eyebrows; they aid in normal tear drainage; and, when used in children, they help stimulate normal growth of the orbital bones.
Even though an artificial eye can be made which has a very realistic appearance, prior to the present invention such artificial eyes have failed to track in conjunction with the normal eye because there was no coupling between the artificial eye and the orbital implant. The artificial eye drifted within the socket and did not track with the normal eye. This lack of tracking was quite apparent and disconcerting to even a casual observer, creating a sense of self-consciousness on the part of the patient. Because of this shortcoming of traditional implants, efforts have been made to attach the eye muscles to the implant and then to attach the artificial eye to the implant. This provided adequate tracking of the artificial eye. However, the success was short-lived because, in a brief period of time, the implant was extruded from the orbit. This implant extrusion occurred because the fixing of the artificial eye to the implant material exposed the implant to the outside environment. This permitted bacteria to enter, and the implant became chronically infected. This exposure was considered necessary, however, to produce an attachment between the implant and the artificial eye.
A wide variety of other materials have been used for orbital implants, such as ivory spheres, gold globes, silk, catgut, acrylic plastics or silicones, human bone (G. C. Sood et al., International Surgery, (1970) Vol. 54, No. 1, p. 1); and antigen-free cancellous calf bone, so called "Kiel Bone," (A. C. B. Molteno, et al., Brit. J. Ophthal., (1973) Vol. 57, p. 615 and A. C. B. Molteno, Trans: of the Ophthal. Soc, New Zealand (1980) Vol. 32, p. 36. These other materials, however, did not provide for significant integration of tissue and vascularization of the implant itself. As described in U.S. Pat. No. 4,976,731, these materials which did not permit significant integration of tissue were disadvantageous in that, when the surrounding tissue heals, the patient risked chronic infection as a result of subsequent procedures necessary to connect the implant to the artificial eye so as to provide tracking of the artificial eye. Also, the weight of the artificial eye was not supported by the implant. This lack of support puts pressure on the lower lid causing lower lid sagging.
A porous orbital implant overcomes these problems. One type of porous orbital implant is described in U.S. Pat. No. 4,976,731. U.S. Pat. No. 4,976,731 issued 11 Dec. 1990 in the name of the inventor herein, Arthur C. Perry; this patent is incorporated by reference in its entirety. The term integrated is used to denote a porous structure capable of containing fibrovascular ingrowth into its pores whether or not such ingrowth has occurred. In the 4,976,731 patent, the use and preparation of an orbital implant comprising hydroxyapatite is described. The use of porous hydroxyapatite allows integration of the implant with fibrovascular tissue. These porous hydroxyapatite implants ("PHA" implants) are described in the 4,976,731 patent, as providing advantages over other implant materials particularly because such integration of the patient's own tissue allows coupling of the implant to the artificial eye, as well as increased long-term stability of both the artificial eye and the implant.
In the past, unevenly textured surfaces of orbital implants have required coating so that the surface is smooth and slippery, so as to allow for facile insertion of the orbital implant into the eye socket. Uneven or roughly textured surfaces, such as the surface of a hydroxyapatite orbital implant, may cause trauma to or otherwise tear tissue surrounding the eye socket where the implant is to be inserted. An uneven or rough textured surface does not allow the implant to be placed deeply into the orbital socket. This problem has been addressed by using homologous or autologous materials, such as human or animal sclera, fascia, or dura for a coating. See, U.S. Pat. No. 4,976,731 which describes, for example, the use of the patient's own scleral sac in the case of an eviscerated eye (in which all the inner contents of the eye have been removed). If the eyeball has been enucleated (removal of the entire eyeball after severing it from the eye muscles and the optic nerve), other material must be used for coating the orbital implant. Materials such as scleral sacs obtained from cadavers or from eye banks, collagen tissue obtained from tissue banks or from animals, or autologous tissue, from another area of the patient's own body have been used.
These coating materials may be difficult to obtain or use. For example, scleral sacs obtained from eye banks may be unavailable in some geographic locations. Moreover, these materials may facilitate the transmission of human or animal disease. Human tissues, in particular, may be capable of transmission of such disease as hepatitis or Acquired Immune Deficiency Syndrome (AIDS). Moreover, some of these materials are perishable, and thus must be transported rapidly and used rapidly. If autologous tissue is used, there is, of course, a certain amount of trauma to the patient himself because another invasive operation is required. Typically with the use of human or animal tissue for coating orbital implants, the surgeon must perform such wrapping immediately prior to the implantation, thus, the time of surgery is lengthened and the time the patient must be under anesthesia is prolonged. Accordingly, large-scale production of pre-coated orbital implants has been impracticable and unavailable.
As a result of the shortcomings of prior implants, there also exists a need for means to improve the vascularization of integrated orbital implants. As set forth above, integrated orbital implants, for example, those comprised of hydroxyapatite, allow vascularization of the implant itself. In a certain percentage of the patients (about three to five percent), however, vascularization is impeded or inhibited for no known reason. In addition, an increased rate or degree of vascular integration into the orbital implant may benefit patients by allowing a faster fitting of an artificial eye.
The advantages to improved vascularization, either in terms of rate of penetration, or the density of blood vessels formed per unit volume, are clear: means to attach the orbital implant to the artificial eye (and thereby provide means for smooth movement of the artificial eye) may occur sooner; and, the strength of the coupling of the orbital implant to the surrounding muscle and scar tissue may be enhanced. With increased vascularization, implant migration and extrusion is decreased. Integration of the tissue is extremely important to properly hold the implant in place.
Concerning coating materials for orbital implants, there is an unmet and long felt need for an orbital implant coating material which is not capable of disease transmission, which causes no detriment or undue trauma to the recipient of the orbital implant, which can be stored and used later without significant problems of perishability, which can be practicably produced in conjunction with the orbital implant itself, which does not lengthen the operation or unduly prolong the time the patient is anesthetized, and which provides a smooth, even surface for the orbital implant.
Therefore, there also exists a need for improved means for vascularization of integrated orbital implants. This improved means for vascularization may be associated with the orbital implant coating, or associated with the orbital implant itself or, as an ongoing therapy.